Design of a radiation pattern reconfigurable antenna for electronic toll collection in intelligent transport system

DESIGN OF A RADIATION PATTERN RECONFIGURABLE ANTENNA FOR ELECTRONIC TOLL COLLECTION IN INTELLIGENT TRANSPORT SYSTEM CHO T Hoang Thi Phuong Thao1,2, Vu Van Yem2 1Electric Power University, 2Hanoi University of Science and Technology 4 1. INTRODUCTION directions. However, the bandwidth of this antenna is narrow. A planar printed With the rapid development of wireless dipole antenna with reconfigurable pattern communication, pattern reconfigurable properties in [10] is able to archive two antenna has received a considerable opposite directions by switching four PIN amount of attention in recent years. diodes. This antenna has high gain, but Pattern reconfigurable antenna is known increase in the overall antenna dimensions. characteristic can adapt with changing system requirements or environmental In this paper, we propose a radiation conditions [1]. A pattern reconfigurable pattern reconfigurable antenna based on antenna can provide different radiation printed dipole structure which can operate patterns, so it can replace a number of at 5.8 GHz band for Electric Toll traditional single antennas in system [2]. Collection (ETC) in Intelligent Transport Therefore, compared with traditional System (ITS). This antenna includes five elements connected or disconnected by antennas, the advantages of PIN diodes. A conventional surface reconfigurable antennas are multifunction, reflective structure is applied under the flexibility, and help to reduce cost and ground of the antenna for gain overall size of system [3]. Furthermore, enhancement. because of adjustable radiation patterns, reconfigurable antenna can be directed By switching these diodes, the antenna toward the access point, so it can save can operate at three configurations with power for transmission and reduce noise beam- [4]. without change in resonant frequency. The bandwidths in any configurations So far, there is a lot of researches on achieve about 200MHz which is suitable radiation pattern reconfigurable antennas for ETC applications. Overall dimension with different techniques, in which PIN of the antenna is 40 × 60 × 13 mm3. The diode is used popularly. In [5], radiation antenna archives gain above 5.37 dBi in pattern of a compact planar antenna can three configurations. be switched from different directions using PIN diodes, whereas in [6], it The remainder of the paper is organized can steered between bidirectional and as follows. Section 2 describes the unidirectional. In [7, 8], the proposed antenna design. Section 3 presents antennas can switch between simulation and measurement results with omnidirectional pattern and directional some discussion. Finally, the conclusion pattern by controlling PIN diodes. of the paper is given in Section 4. Another radiation pattern reconfigurable 2. ANTENNA DESIGN antenna using PIN diode is proposed in [9] can select between two beam The structure of the proposed antenna is given in figure 1. The antenna includes full copper surface which is used for gain the main radiation part and the reflector. enhencement. The antenna achieves the best simulated gain when the distance The main radiation part of the antenna looks like an array of five printed dipoles from the substrate to the copper is 13 mm. The substrate of antenna has the thickness with each dipole placed on front side and h=1.6 mm, the relative permittivity =4.4 back side of the substrate. These dipoles r are fed via a central transmission line. The and the loss tangent = 0.02. The overall transmission line with two microstrip size of antenna is 40 mm × 60 mm × 13 mm. lines are designed on the opposite sides of a dielectric substrate. The reflector is a Figure 1. Antenna structure: dark lines on the front side of the dielectric substrate, transparent ones on the back (front view and side view) The width of the transmission line is 120 Z chosen to ensure the input impedance at 0 WW 1.393 0.667ln 1.444 fed point to be 50 e h h line is on two side of the substrate, it is (1) with the width of W and the substrate where Z0 is impedance of the transmission thickness of h/2. We can calculate the line (25 is effective permittivity of width of transmission line from the e equation (1) [11]. transmission line given approximately by: 1 isolate AC current from the DC bias line 1 1 12h 2 r r system which is used to control PIN e 1 (2) 2 2 W diodes. Five SMP1345 PIN diodes are The length of a single dipole for a used to obtain three operating states. These PIN diodes can operate within a designed resonant frequency fr is: frequency range from 10 MHz to 6 GHz c and have equivalent circuit depicted in LD (3) 2 fr e figure 2. The operations of the PIN diodes at three states are given in table 2. In each where c is the speed of light in free-space. state, only two dipoles distanced e/4 Now, we compute the width Wd of the operate. It means that the distance of the dipole. We select the dipole characteristic two operating dipoles in three states is the same while the difference in phase transmission line. To achieve the excitation between the ones are different, characteristic impedance Zin which helps to adjust the total radiation radius of the cylindrical dipole is field of the antenna. These phase computed by the equation (4) [12]: differences in state S1, S2, S3 are 0, /2; /2. The electrically equivalent shapes LD of the antenna at different configurations Zin 120 ln 2.25 (4) aD are given in figure 3. Table 1. Dimensions where aD is the radius of the cylindrical of the proposed antenna (mm) dipole, LD is the length of the dipole. For printed dipole, its width Wd is calculated Ld Wd W D Wa La Ha [13]: 16.6 1 3 8.8 40 60 13 Wd= aD (5) Table 2. Operation of PIN diodes Also, the distances between the elements are selected so that two operating dipoles State D1 D2 D3 D4 D5 are distanced e/2 in each operating state, S1 OFF ON OFF ON OFF which is detailed below. . S2 ON OFF ON OFF OFF Based on initial dimensions, the antenna S3 OFF OFF ON OFF ON is optimized again by CST simulation In the state S1, diode D2 and D4 are ON, software. The dimensions of the proposed the remaining diodes are OFF. Therefore, antenna are shown in table 1. only element L2 and L4 are connected to In oder to achive radiation parttern transmission line. The antenna is in a reconfiguation, PIN diode switchings are symmetric topology. The phases of the used. PIN diodes are controlled to ON waves which are fed to the two main or OFF to achieve different radiation radiating elements are the same, thus the patterns with the same frequency of main lobe is perpendicular to the antenna 5.8 GHz at all states. Inductors are used to plane. In the state S2, diode D1 and D3 are ON, the remaining are OFF, elements L1 and L3 are connected to the transmission line. The phase of the wave fed to element L3 is /2 earlier than that to L1. Therefore the main lope is skewed towards the element L1. (a) State 1 (b) State 2 (c) State 3 Figure 3. Equivalent configurations in three states The state S3 is similar to the state S2 but bandwidth is very suitable for ETC the radiation pattern reconfigured to other applications. direction. In this state, diode D1 and D3 are ON and the remaining are OFF. The operating elements are L1 and L5. The main lope is toward the element L5. 3. RESULTS AND DISCUSSION This section presents the simulation and measurement results of S11 parameter as well as the simulation radiation pattern. The S11 parameter and the radiation properties of the proposed antenna are simulated by the combination of CST Figure 4. Simulation results of S11 parameter Microwave and CST design software. in all states of the proposed antenna Simulation results of S11 parameter are The simulation radiation patterns of the shown in figure 4. It can be seen clearly antenna with different configurations are that all configurations produce the same plotted in figure 5 and figure 6. By resonance frequency of 5.8 GHz with switching diodes, the pattern characteristic -10 dB bandwidths about 200 MHz. This is reconfigured between three different directions. The axis of the maximum gain State 2 is shifted at an angle of 60o degrees when changing the configuration of the antenna. The simulation gains in state S1, S2, S3 are 5.37, 6.34, and 6.09 dBi respectively. State 3 Figure 5. Simulation results of 2D radiation pattern in all states of the antenna State 1 Figure 6. Simulation results of 3D linear radiation pattern in all states of the proposed antenna Table 3 summarizes all simulation results of the proposed antenna, including the resonance frequency, the bandwidth, the beam-steering angles, the 3dB angular width as well as the maximum gain in each state. Table 3. Summary of simulation results in all states of the proposed antenna. State Resonance Bandwidth Beam-steering Angular width Peak Gain Frequency (GHz) (MHz) angles (degree) (3dB) (degree) (dBi) S1 5.8 195 0 103 5.37 S2 5.8 200 60 58.2 6.34 S3 5.8 195 -60 58.1 6.09 4. CONCLUSION pattern reconfigurable dipole antenna This paper presents a novel radiation using PIN diode for Electric Toll Collection in Intelligent Transport With this approach, we are able to design System. By switching diodes placed on radiation pattern reconfigurable antenna radiation elements, the antenna archives operating in desired frequencies for three different radiation patterns while difference applications. The proposed maintaining the resonance frequency of antenna is designed on FR4 and simulated 5.8 GHz with the bandwidth about and optimized by the combination of CST 200MHZ at three configurations which is microwave and CST design software. very suitable for ETC application. The Because of lack of anechoic chamber, the peak gain of antenna in three antenna radiation pattern has not been configurations is in turn 5.37, 6.34, and measured yet. In the future, we will do 6.09 dBi. The antenna is a suitable measurements in radiation pattern to candidate for smart radio in the future. confirm with the simulation results.